This research will study the relationship between sexually dimorphic reproductive behavior patterns and sexually dimorphic neuronal connectivity patterns in the central nervous systemof the golden hamster (Mesocricetus auratus). Adult dendritic patterns will be described in male and female hamsters in the preoptic area, suprachiasmatic nucleus, anterior hypothalamus, filiform nucleus, and possibly other areas for which functional dimorphism may be suggested. Male-female comparisons will be made using a sensitive quantitative analysis of Golgi-stained brain tissue from these areas. The relationship between the neuroanatomical measures and behavior will be examined by manipulating neonatal hormones of both genetic males and genetic females (through neonatal gonadectomy and hormone treatment). These neuroanatomical measures will be correlated with measures of masculine and feminine behavior as defined in intact normal genetic males and females. Based upon these findings, the development of apparent sex differences will be traced by sampling brain tissue during the period of sexual differentiation in this species. Patterns of neuronal connectivity in neonatally manipulated animals (as above) will also be examined developmentally. Ultimate goals of this work are to understand ways in which hormones may specify or influence nerve connections and to relate the dimorphic "wiring diagram" of basal forebrain regions to dimorphisms in reproductive behavior. Preliminary results are reported describing quantitative sexual dimorphism in dendritic densities in the dorsomedial preoptic area and suprachiasmatic nucleus in the hamster.